Summary

• Updates buildGroupChatContext so normal group text replies remain direct/automatic, while files, images, and attachments may use the message tool targeting the same group.
• Updates focused prompt coverage so the old blanket same-group message-tool ban cannot regress.
• Carries forward the useful work from fix(auto-reply): allow message tool for attachments in group-chat sessions #43276 by @NayukiChiba and Auto-reply: allow message tool for non-text content #48004 by @ShakaRover with attribution.

Validation

• pnpm check:changed

Closes #43146.
Source PR credit: #43276 and #48004.

Clownfish 🐠 replacement reef notes:

• Cluster: ghcrawl-157067-autonomous-smoke
• Source PRs: fix(auto-reply): allow message tool for attachments in group-chat sessions #43276, Auto-reply: allow message tool for non-text content #48004
• Credit: Credit @NayukiChiba for source PR fix(auto-reply): allow message tool for attachments in group-chat sessions #43276, which identified the exact buildGroupChatContext prompt conflict and added focused tests.; Credit @ShakaRover for source PR Auto-reply: allow message tool for non-text content #48004, which contributed the non-text/media allowance direction and review discussion about clearer attachment wording.; Mention that Clownfish is carrying the closed source PR work forward because both branches are closed/uneditable for automation.
• Validation: pnpm check:changed

fish notes: model gpt-5.5, reasoning medium; reviewed against 664582b.